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17 keeps fouling plugs

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We got a 17 250x here that's fouled ten plugs. We finally changed jetting to one step leaner on each. Can't remember right now exactly the numbers. Running 50:1 Amsoil dominator. She still fouls plugs in the middle of a ride. Not much lugging. Why?? What's going on here!?! 1000m. 20c

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Check that the float / fuel level is set to the service manual's specs.

it's actually quite common for brand new bikes to have this setting too high.

 

If you mostly trail ride, Dominator, a high flash point racing premix may not be ideal for your usage.

Interceptor would no doubt be better suited.

Edited by mlatour
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No we havnt. I've fiddled with a lot of carbs. But that's something I havnt done yet.

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Well. We adjust the float inwards a tinyyyyy bit. Started it. And it fouled another plug.

IMG_1874.JPG

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Check your air screw and see if it's where it's supposed to be from factory. My 16  is running stock jetting and doesn't come close to fouling plugs.

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What to you means adjusted the float 'inward' ?

If you meant you bent the needle's tab so the float is now closer to the carb's body,

you raised the fuel level and likely have made things worse.

Edited by mlatour
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What to you mean by adjusted the float 'inward' ?
If you meant bend the needle's tab so the float is closer to the carb body,
you raised the fuel level and likely have made things worse.

Hahaha, I didn't want to say anything.

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Yeah I think we did it backwards. Bent it a tad the other way and seems to run better so far haha!! Never messed with floats before

The air screw is that tiny little flathead brass one that's tough to get at?

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Stop guessing, quite honestly it sounds like you need to start consulting the service manual....

 

All the answers plus, 90% of all your future questions will be answered in there.

Yamaha manuals have a really nice jetting charts, suggested changes for ambiant temps etc.

Edited by mlatour
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Fouled plugs means the burn (on each power stroke) is incomplete for some reason. Typically rich jetting, but what caused it to get richer if it once worked ok? Hotter air temps? High altitude? Clogged air filter? Clogged muffler? Changed fuel?

You could also have a leaking ride side crank seal. Does the exhaust smoke smell like something not simply premix oil?

Or maybe you have a weak spark.  Coil, lead, plug cap, stator, damaged CDI, etc.

If you get a complete burn then you can use a thick oil like 800T or 927 castor at 40:1 and lug it every ride and never foul a plug or have a spooge drip out the muffler exit. Just a tiny puff of premix smoke at times.  But I'm not sure if it's always possible to get a complete burn at all throttle positions using the stock Yamaha needle.

Edited by numroe

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Stock jetting tends to be set up for Sea Level altitude and stock premix ratio.

Most obvious issues are 1000m altitude and 50:1 premix ratio. If your stock premix ratio was 40:1 or 32:1, then you need to lean out the carb for both the ~3000ft altitude and more fuel in the 50:1 premix.

Probably means it needs smaller pilot and main jets and dropping the needle (raising the clip).

 

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